An Amtrak train heading from Santa Barbara to Ventura passe by part of Ventura County's Thomas Fire

Firefighters say the massive Thomas brush fire in Ventura County took another big jump in size on Wednesday, and has the potential to grow rapidly with the potential for a dangerous new round of Santa Ana winds in the weather forecast.

The fire went from 65,000 to 90,000 acres burned, with containment at 5%

The number of structures destroyed hasn’t been updated from Tuesday’s reported 150, but that number could grow when ground teams complete mapping of hard hit areas.

National Weather Service meteorologist Rich Thompson says Thursday poses the most challenging day for the remainder of the week weather wise, with the potential for major growth of the fire. Santa Ana winds could hit 50 miles an hour, with low humidity. Firefighters are especially concerned about the potential threat to the Oak View, and Ojai Valley areas.

The number of people evacuated by the fire now tops 50,000 people, and firefighters credit people following evacuation orders with preventing a large scale loss of life, and injuries. 12,000 structures are still considered to be in the potential danger zone.

Despite the concerns about the fire, firefighters say they made substantial progress towards containment of the blaze on multiple flanks of the fire. Containment went from zero to 5%. The blaze began Monday night, off of Highway 150 between Santa Paula and Ojai.

The massive Thomas Fire has now charred 65,000 acres of land in Ventura County, and is still completely out of control.

The blaze covers 100 square miles of land. 150 structures have been reported destroyed by the fire, but that figure hasn't been updated since Tuesday morning, and could change. 12,000 structures are considered to be at risk, and close to 30,000 people are facing evacuation orders.